Defense Minister Adrian Tutuianu said Romania's Parliament first needs to pass a law that would allow the acquisition. Tutuianu estimated Romania could begin paying for the missiles by November.

His comments were the first time a Romanian official has publicly provided details of the proposed deal.

FILE- In this Sunday, July 16, 2017 file photo, Romanian soldiers take part in a joint exercise with US troops during Argedava Saber 17, a stage in Saber Guardian 17 exercises, in Bordusani, Ialomita, Romania. Romania's defense minister has confirmed that the country intends to buy Patriot missiles worth $3.9 billion dollars from the United States. (AP Photo/Andreea Alexandru, File)

The U.S. State Department approved the sale this month, saying it would help to "improve the security of a NATO ally.... that is an important force for political stability and economic progress within Europe."

The State Department said the missile system would strengthen Romania's "homeland defense and deter regional threats," ''increase the defensive capabilities of the Romanian military," and "shield the NATO allies" that often train in Romania.

The U.S. increased its presence in Eastern Europe with regular training exercises to reassure NATO's European allies after Russia annexed Ukraine's Crimea Peninsula in 2014.